ACTION OF LIGHT ON MICRO-ORGANISMS 349 



than the B. prodigiosus. The anthrax bacillus was 

 destroyed in four or five hours when exposed on 

 potatoes, and in six or seven on gelatine. Pansini 

 further found that this effect was due to the action of 

 light on the bacteria and not on the culture material, 

 for if the latter after this exposure was re-inocu- 

 lated it was found to have lost none of its nutritive 

 capacity. 1 



The chief novelty of Pansini's experiments lies in 

 the more exact information they give us as to the 

 rapidity at which bacteria are destroyed by the agency 

 of light. 



For this purpose, drop cultures of the various 

 organisms were prepared in the usual manner, and after 

 they had been insolated for a definite length of time the 

 cover-glass was carefully removed and placed in melted 

 gelatine, and after thorough agitation in order to insure 

 the equal distribution of the organisms as well as 

 to effect their entire removal from the surface of the 

 cover- glass, plates were poured in the usual manner 

 and the resulting colonies counted. As an example of 

 the results obtained the following experiment may be 

 cited : Drop cultures were prepared of a young cul- 

 ture of the B. anthracis, 2 and exposed to sunlight for 

 periods of time varying from ten to seventy minutes, 

 during which the temperature ranged between 32 and 

 40 C. From the cover glass kept in the dark 2,520 

 colonies were obtained on the following day on the 

 plates poured, whilst none had appeared on the plates 



1 The writers have been unable to ascertain what were the particular 

 microbes referred to by Pansini as having been re-inoculated on to the 

 various insolated media and found capable of growing. It will be re- 

 membered that Roux found that the bacilli of anthrax were able to 

 develop in insolated bouillon, but not the spores. 



2 There is no guarantee that spores were not present, as no special pre- 

 cautions were taken to exclude them. 



